This is a proposal to demonstrate the accuracy and resolution with which one can define myocardial infarction and ischemia using the positron emitting isotope rubidium-82 and carbon-11 amino acids and fatty acids. Rubidium-82 (75 sec half-life) is available from a table top generator containing strontium-82 (25 day half-life). The detection system is comprised of 280 rectangular crystals 8 mm wide mounted on a circle of 90 cm diameter. Transverse sections are obtained for 100 msec intervals of the cardiac cycle using eight memories and the EKG R-wave. Experimental work will be with phantoms designed to simulate a beating heart within the thorax and with canine infarct preparations. Animal studies of acute infarction include in vivo measurements of the incorporation of branched-chain amino acids and palmitic acid in the myocardium. In addition, confirmation studies will be performed with ambulatory patients. The system we propose to use has the highest resolution and speed of any positron imaging system in the world for the accumulation of transverse sections of heart at 100 msec intervals. Use of rubidium-82 allows us to non-invasively image the myocardium repeatedly with sufficient resolution and sensitivity to detect 50% changes in myocardial perfusion in 1 cm3 volumes with a radiation dose to the whole body of less than 20 mrads per 10 mCi injection.